dopamine (a catecholamine) and serotonin are produced from a singe aminoacid: tyrosine/tryptophan. The first step is the synthesis of DOPA, dihydroxyphenylalanine by tyosine hydroxylase. Then DOPA is decarboxylized by DOPA decarboxylase to yield dopamine.

Serotonin is made from tryptophan in the following way: first there's a hydroxylation by tryptophan - 5 - hydroxylase. Then the product is decarboxylized to yield serotonin.